Afocal front attachment for photographic or cinematographic objectives



390549327 JOWT WHT Sept 18, 1962 w. ALBRECHT ETA.

AFocAL FRONT ATTACHMENT FOR PHoTo CINEMATOGRAPHIC OBJECTIVES Flled Allg. 15, 1959 M f, 3 l n f l /f L ,w 1 J I .mv B u United States Patent O 3,054,327 AFOCAL FRONT AITACHIVIENT FOR PHOTO- GRAPHIC OR CINEMATOGRAPHIC OBJEC- TIVES Wolfram Albrecht, Kreuznach, Rhineland, and Werner Wagner, Odernheim (Glan), Germany, assignors to Jos. Schneider & Co., Optische Werke, Kreuznach, Rhineland, Germany, a corporation of Germany Filed Aug. 13, 1959, Ser. No. 833,590 Claims priority, application Germany Sept. 16, 1958 6 Claims. (Cl. 88-57) Our present invention relates to an afocal front attachment adapted to increase the effective thereby or cinematographic objective.

Front attachments of this type, used frequently (but not exclusively) on 8-mm. motion-picture cameras, conventionally consist of was to be maintained.

The general object of our vide a relatively simple front and distortions.

A front attachment according to our invention consists of a four-lens front component and a two-lens rear comfocal length of the front component.

We have also found it desirable to select the glasses of the four lenses of the front component in such manner that the arithmetic mean of their refractive indices ranges between a minimum of 1.6 and a maximum of 1.75.

A system satisfying the above conditions has been found free from objectionable aberrations and, in particular, is highly achromatic so as to be especially suitable for the taking of color lilms.

The invention will be described in greater detail with reference to the accompanying drawing in which FIGS.

ponents being separated from each other by a relatively large air space d6 (as compared with the intra-component spacings). An associated principal objective has been indicated schematically at O; its image plane is shown at B.

The front component I consists of four lenses L1, La, L3 and L4. Lens L1, having radii r1, r11 and thickness d1, is a singlet in the form of a positive meniscus separated by an air space d, from a similarly meniscus-shaped triplet constituted by the remaining three lenses L2 (radii r3, r, and thickness d3), L3 (radii r4, f5 and thickness d1), and L1, (radii f5, rs and thickness d5). The rear component II consists of a positive singlet L5, with radii f7, rs and thickness dq, and a negative singlet L, separated from lens L5 by an air space d, and having radii r9, r11, and thickness dg.

Representative numerical values of the radii, thicknesses and separations of lenses L1 to Ls (in millimeters), of their refractive indices nd and of their Abb numbers u are given in the following Example A for a front attachment designed to co-operate with a camera objective having a focal length of 13 mm. and an aperture ratio of 1:1.8.

EXAMPLE A Thicknesses and Air Spacngs Lens Radil air space air space air space The relationship between the focal length f1 of the front component I, the focal length fn of the rear component II, the focal length f1 of front lens L1, and the radii r1, r3 and r1 of the system of FIG. 1 are listed in the following Table 1 which also gives the mean of the refractive indices n1 to n1 of the lenses L1 to L1 of the front component.

Table I 3 Table I-Continued r3 =0.70 f1 |f4l'=4.72 fr the fourth lens of the front component I is a meniscusshaped positive singlet L4', having radii r6', rq and thickness ds', which is separated from doublet L2'/L3 by an air space d5'. It will be noted that the configurations of lenses L2', L3' and L4 are also similar to those of the corresponding lenses in FIG. 1. Front component I' is separated by a large air space dq' from the rear component II' in which a nearly plano-convex positive lens L5' (radii ra', r9' and thickness da) and a biconcave lens La' (radii r9', rm and thickness dg'), each similar to the corresponding lens of FIG. l, are cemented together to form a doublet.

Representative numerical values of the radii, thicknesses and separations of lenses L1 to Ls (in millimeters), of their refractive indices nd and of their Abb numbers v are given in the following Example B which concerns a front attachment designed to co-operate with the same type of objective as that described in connection with Example A.

EXAMPLE B Thicknesses and Air Spac s Radil mg v air space air space air space The relationship between the focal length f1' of the front component I', the focal length fn' of the rear component II', the focal length f1' of front lens L1', and the radii r1', r3 and r4 of the system of FIG. 2 are listed in the following Table 2 which also gives the mean of the refractive indices ny to n4' of the lenses L1' to L4 of the front component.

Table 2 Although the linear parameters in the foregoing examples have been given in millimeters, it will be understood that these examples are equally valid for other units of 4 length and that departures from the exact numerical values set forth therein, with adherence to the aforestated relationships between the focal length of the front component, the focal length of the front lens and certain radii of the rst three lenses, are permissible within the spirit and scope of the invention as dened in the appended claims.

We claim:

1. An afocal front attachment for an optical objective, consisting of a positively refracting front component and a complementarily negatively refracting rear component, said front component being composed of a positive first, a positive second, a negative third and a positive fourth lens, said rear component being composed of a positive fifth and a negative sixth lens, at least said second and third lenses being cemented together and air-spaced from said rst lens, said first lens and the member formed by said cemented lenses being each in the form of a positive meniscus having a respective convex surface turned toward the object side of the system, the cemented surface between said second and third lenses having a radius ranging between 3 and 5 times the focal length of said front component, said rst lens having a focal length ranging between 1.5 and 2.5 times the focal length of said front component, the radius of the convex surface of said first lens turned toward said object side is greater than four-fifths but less than the whole of the focal length of said front component, the radius of the convex surface of said cemented member turned toward said object side ranges between 0.6 and 0.9 times the focal length of said front component, and the arithmetic mean of the refractive indices of said first, second, third and v fourth lenses ranges between 1.6 and 1.75.

2. An attachment according to claim 1 wherein the cemented surface between said second and third lenses has a radius ranging between 3 and 5 times the focal length of said front component.

3. An attachment according to claim 2 wherein said fth and sixth lenses are air-spaced from each other.

4. An attachment according to claim 3, adapted to cooperate with an objective system having a focal length of 13 units of length, wherein the radii r1 to rm of said first through sixth lenses and the thicknesses and separations d1 to dg thereof, given in said units of length, as well as the numerical values of their refractive indices nd and their Abb numbers v are substantially as listed in the following table:

l5. An attachment according to claim 2 wherein said fifth and sixth lenses are cemented together.

6. An attachment according to claim 5, adapted to co-operate with an objective system having a focal length of 13 units of length, wherein the radii r1 to -rm of said first through sixth lenses and the thicknesses and separations d1' to d, thereof, given in said units of length, as well as the numerical values of their refractive indices nd and their Abb numbers r are substantially as listed in the following table:

Thicknesses and Air Spacings Lens Radi v n -+34.72 L1' d1=8.24 1. 62041 60. 3

d,=0.35 air space ra' =+33.68 Lg' dz =8.l54 1. 69350 63. 4

r4' --14208 L.' d4' -1.93 1. 69895 30. 1

d;=0.18 air space n +2113 L.' d. =7.65 1. 60311 60. 7

d1 =6.11 air space n' =+1,58S.00 Ll d;=5.07 1. 58144 40. 8

n' =l10.61 L.' d.' =1.01 1. 58313 59. 3

TMI-F814 References Cited in the le of this patent UNITED STATES PATENTS 

